Solvent extraction of platinum group metals

ABSTRACT

This invention relates to the separation and purification of the platinum group metals; more particularly it relates to the separation of mixtures of Pt and/or Pd from Rh and/or Ru. 
     In more detail, the present invention relates to a process for the separation or purification of platinum group metals in which either platinum, iridium (IV) and/or palladium (II) are present in aqueous solution together with one or more other platinum group or base metals comprising the steps of: 
     (a) adjusting the acidity, if necessary, to provide a pH less than 7; 
     (b) contacting the said aqueous solution with an organic phase containing at least one nitrogen containing organic compound selected from the group consisting of primary, secondary and tertiary amines and quarternary ammonium compounds and at least one oxygen containing organic compound selected from the group consisting of alcohols, phenols and carboxylic acids; 
     (c) removing from contact with the said solution the said organic phase now containing the platinum, iridium (IV) and/or palladium (II) extracted together with the nitrogen- and oxygen-containing organic compounds; and 
     (d) contacting the organic phase obtained at stage (c) above with a strongly acidic solution and thus stripping the platinum, iridium and/or palladium from the said organic phase and obtaining an aqueous solution of the said metals.

This is a continuation of application Ser. No. 213,489 filed Dec. 5, 1980, now abandoned.

This invention relates to the separation and purification of the platinum group metals; more particularly it relates to the separation of mixtures of Pt, Ir and/or Pd from Rh and/or Ru.

In the recovery and separation of the platinum group metals from mineral deposits it is frequently necessary to separate and purify Pt, Ir and/or Pd from aqueous solutions also containing salts of Ru and Rh together with small quantities of dissolved base metals such as Fe, Cu, Ni and Se present to the extent of up to 5% by weight.

Examples of such processes involving separation and purification are described in U.S. Pat. Nos. 3,960,549 and 3,979,207. The present invention, which constitutes a modification and improvement in the inventions described in the above-mentioned specifications, is also applicable wherever it is desired to recover Pt or Ir by solvent extraction.

In the solvent extraction process described in U.S. Pat. No. 3,960,549, the solution is preferably acidified at stage (a) with hydrochloric acid to establish an HCl strength within the range 3-9 M, preferably about 6 M. In order to prevent any Ir(IV) present being extracted with the Pt, chemical reduction of the Ir to Ir(III) is then effected. The Pt is then extracted by the use of a tertiary amine extractant such as Alamine 336. The Pt is preferably stripped from the Alamine 336 by the use of an alkaline stripping solution. Alkali metal hydroxides, carbonates or bicarbonates or ammonium hydroxide were recommended for this purpose. Similar considerations apply later in the process to the Ir. When the Ir is re-oxidised to Ir(IV) it will be extracted equally effectively with a tertiary amine such as Alamine 336. The organic compounds are then preferably stripped with alkali. In the alternative process described in U.S. Pat. No. 3,979,207, Pt and Ir(IV) are extracted together by the same reagent.

In either case the platinum group metal is then recovered from the alkaline strip liquor. This is a wasteful operation. The present invention, which constitutes a substantial improvement over the prior art processes enables both extraction and stripping to be carried out in an acidic medium. We have now found that certain modifiers used in conjunction with specified nitrogen containing organic compounds enable platinum, palladium and/or iridium (IV) to be both extracted and stripped in an acidic environment.

According to one aspect of the present invention a process for the separation or purification of platinum group metals in which either platinum, iridium (IV) and/or palladium (II) are present in aqueous solution together with one or more other platinum group or base metals comprises the steps of:

(a) adjusting the acidity, if necessary, to provide a pH less than 7;

(b) contacting the said aqueous solution with an organic phase containing at least one nitrogen containing organic compound selected from the group consisting of primary, secondary and tertiary amines and quarternary ammonium compounds and at least one oxygen containing organic compound selected from the group consisting of alcohols, phenols and carboxylic acids;

(c) removing from contact with the said solution the said organic phase now containing the platinum, iridium (IV) and/or palladium (II) extracted together with the nitrogen- and oxygen-containing organic compounds; and

(d) contacting the organic phase obtained at stage (c) above with a strongly acidic solution and thus stripping the platinum, iridium and/or palladium from the said organic phase and obtaining an aqueous solution of the said metals.

In stage (a), if the aqueous solution does not already have a pH less than 7, it is preferably acidified with hydrochloric acid to establish a hydrochloric acid strength within the range 0.1-1 molar, preferably about 0.3 molar. At stage (a) the chloride concentration of the solution should be relatively low, preferably within the range 0.1-1.0 molar.

In step (b), the preferred nitrogen containing organic compound used is a branched chain secondary amine of general formula R₂ NH in which R is aliphatic, preferably C₁₂ -C₁₄ alkyl. Iso-alkyl groups may also be used in the secondary amine, however, and the R groups may therefore be the same or different and selected from the group comprising the normal and iso isomers of hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl alkyl groups.

Examples of commercially available secondary amines which may be used are:

(a) N-dodecyl (trialkylmethyl) amine (Amberlite LA 1)(Registered Trade Mark); a secondary amine supplied by Rohm & Haas having a molecular weight within the range 351-393);

(b) N-lauryl (trialkylmethyl) amine (lauryl═dodecyl) Amberlite LA 2 (Registered Trade Mark); a secondary amine supplied by Rohm & Haas having a molecular weight within the range 353-395);

(c) Amine 9D-178 (a secondary amine mixture);

(d) Armeens (Registered Trade Mark) and Ethomeens (Registered Trade Mark) supplied by Armour-Hess Chemicals; and

(e) Adogen 283, di isotridecylamine.

Primary amines may be used in step (b) and include those of the type RNH₂ where R is aliphatic, preferably ranging from C₆ -C₃₀. Both normal and iso alkyl groups may be used.

Examples of primary amines which may be used are:

(a) dodecylamine; and

(b) Primene (Registered Trade Mark) and JM-T and 81-R, supplied by Rohm & Haas.

Tertiary amines also may be used in step (b). Suitable tertiary amines include those of the type R₃ N where R is aliphatic. Preferred R groups are normal alkyl ranging from C₆ -C₁₄. Iso-alkyl groups may also be used and the R groups may, therefore, be the same or different and selected from normal or iso isomers of hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl alkyl groups.

Examples of tertiary amines which may be used are:

tri-n-hexylamine;

methyldi-n-octylamine;

tri-n-octylamine;

tri-iso-octylamine;

tri-n-heptylamine;

tri-iso-heptylamine;

tri-n-nonylamine; and

tri-iso-nonylamine.

Quarternary ammonium compounds may also be used in step (b), suitable compounds including those of the type R₄ N⁺ X⁻ where R is preferably aliphatic and is a normal alkyl ranging from C₆ -C₁₄, although iso-alkyl groups may also be used. The R groups may, therefore, be the same or different and selected from normal or iso isomers of hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl alkyl groups. X in the above is preferably halide, for example chloride.

In the above formula, the compound is represented as being a salt of a mono-valent anion. Salts of poly-valent anions such as sulphate, phosphate and the like may also be used, however.

Examples of suitable quarternary ammonium salts are:

methyltrioctyl ammonium chloride;

tetrahexyl ammonium chloride;

tetraoctyl ammonium chloride; and

tetraiso-octyl ammonium chloride.

Aromatic and mixed aliphatic aromatic R group may also be used for the tertiary amine and quarternary ammonium compounds. Examples of such tertiary amines and quarternary ammonium compounds are:

triphenylamine;

tribenzylamine;

diphenyl methylamine;

phenyl trimethyl ammonium hydroxide;

dimethyl benzylamine; and

dimethyloctyl benzyl ammonium chloride.

Examples of commercially available tertiary amines and quarternary ammonium compounds which can be used are:

(a) Arquad 2HT (Registered Trade Mark); a dimethyl dioctadecyl quarternary ammonium chloride;

(b) Ethomeens (Registered Trade Mark) for tertiary amines and quaternary ammonium compounds, mostly water insoluble, supplied by Armour-Hess;

(c) Adogens (Registered Trade Mark; supplied by Ashland Chemicals): Adogen 364 Tri-n-alkylamine, predominantly C₉ ; Adogen 381 Tri-iso octylamine and Adogen 383 tri-tridecylamine;

(d) Alamines (Registered Trade Mark; tertiary amines supplied by General Mills): Alamine 336 Tricaprylamine, predominantly C₈ -C₁₀ (capryl═octyl) Alamine 308, and

(e) Aliquats (Registered Trade Mark) quarternary ammonium compounds supplied by General Mills: Aliquat 336 methyl tri-n-alkyl-ammonium chloride; a quarternary having predominantly C₈ -C₁₀ normal alkyl groups.

In step (b), the nitrogen containing organic compound is preferably equilibrated with an acid, preferably hydrochloric acid, before contacting with the acidified solution.

Oxygen containing organic compounds for use in the organic phase used in step (b) are straight chain, branched chain and cyclic alcohols, straight chain, branched chain and cyclic carboxylic acids and phenols. By "alcohols" we mean to include polyols, e.g. diols, and by "carboxylic acids" we mean to include aromatic acids such as benzoic acids. A list giving examples appears in Table 1.

                                      TABLE 1                                      __________________________________________________________________________                              MOLECULAR                                             CHEMICAL CLASS                                                                            MODIFIER      WEIGHT  NATURAL STATE                                 __________________________________________________________________________     Straight chain                                                                            Hexan-1-ol    108     liquid                                        alcohol    Octan-1-ol    130     liquid                                                   Dodecanol     186     solid m.p. 21°                         Branched   2-Ethylbutanol                                                                               130     liquid                                        Primary    2-Ethylhexanol        liquid                                        alcohol    3,5,5-Trimethylhexanol                                                                       144     liquid                                                   Tridecanol    200     liquid                                        Secondary  Octan-2-ol    130     liquid                                        alcohol    2,6,8-Trimethyl-4-nonanol                                                                    198     liquid                                                   4-Methylpentan-2-ol                                                                          110     liquid                                        Tertiary alcohol                                                                          t-Pentanol     88     liquid                                        Cyclic     Cyclohexanol  100     liquid                                        alcohols   3,3,5-Trimethylcyclohexanol                                                                  142     soldid m.p. 34°                        Straight   Hexanoic acid 116     liquid                                        chain      Octanoic acid 144     liquid                                        acid       Dodecanoic acid                                                                              200     solid m.p. 43°                         Branched   2-Ethylbutyric acid                                                                          116     liquid                                        chain      2-Ethylhexanoic acid                                                                         144     liquid                                        acids      3,5,5-Trimethylhexanoic acid                                                                 158     liquid                                                   Versatic acid 9/11                                                                           172     liquid                                        Cyclo Aliphatic                                                                           Naphthenic acid                                                                              180     liquid                                                   Nonylphenol   220     liquid                                        Phenols    Dodecylphenol 263     liquid                                                   2,4-di-t-butylphenol                                                                         206     solid m.p. 52-57°                      Di-ols     2-Ethylhexane-1,3-diol                                                                       146     liquid                                        Benzoic acids                                                                             p-tertiary butyl benzoic acid                                                                178     solid m.pt. 166-167°                   __________________________________________________________________________

At step (d) the strongly acidic solution is preferably strong HCl solution but other strongly acidic solutions such as HBr and HClO₄ could be used.

Known techniques may be used for ensuring adequate contact of the nitrogen and oxygen containing organic compounds with aqueous solution as described in step (b) and with the strongly acidic solution as described in step (d). If the operation is being carried out on a large scale, a multi-stage counter-current extraction assembly may be used. Alternatively, the two phases may be vigorously agitated together by shaking, stirring, etc.

The invention also includes platinum group metals obtained using the process according to the invention.

The process of the present invention lends itself to operation in a multi-stage counter-current extraction assembly and, accordingly, a further feature of the present invention includes the use of a counter-current extraction assembly for the separation of rhodium, platinum, palladium, ruthenium and iridium as described above.

Feed liquors can vary greatly in their concentrations of platinum group metals.

The invention will now be described with reference to the following examples and the accompanying drawings which graphically show the effect of diluent in the process of the invention.

Example 1-PRELIMINARY INVESTIGATION OF MODIFIERS ON ADOGEN 383

Stock solutions containing 10 gl⁻¹ Pt (IV) in 0.1, 0.3, 0.6, 1.0, 3.0, 6.0 and 10.0 M hydrochloric acid were prepared from sodium hexachloroplatinate (IV) and standardised acid. (H₂ PtCl₆ was used to prepare the 10 M HCl solution due to problems with precipitation of NaCl). Samples (25 ml) of these solutions were contacted with equal volumes of an organic phase as listed in Table 2 for two minutes. The aqueous phases were separated and analysed for platinum by atomic absorption spectroscopy. From the analyses, the concentrations in the organic phase were determined by difference and the distribution coefficients then calculated.

The distribution coefficients given in Table 2 indicate that all the oxygen containing compounds used as modifiers for Adogen 383 reduced its extractive power. Both octanoic and 2-ethyl hexanoic acids, at the 50% (w/v) level (3.5 M) modify the extractive power of Adogen 383 sufficiently to allow acid stripping (D_(A) ^(o) 0.23 and 0.25) (a distribution coefficient of <1, preferably <0.5, being required for efficient stripping) whilst giving sufficiently high distribution coefficients from 0.3-0.6 M HCl (6.9-12 and 8.1-15) for complete extraction to be achieved. Versatic (Registered Trade Mark) 911 acid has a smaller effect which could be due to the fact that it is present at a lower molar concentration (2.9 M). Nonylphenol has a considerably stronger effect than any of the other modifiers and it required only 15% (w/v) (0.7 M) to give a comparable effect to 50% (w/v) (3.5 M) octanoic and 2-ethyl hexanoic acids.

                                      TABLE 2                                      __________________________________________________________________________                         0.1 M 0.3 M 0.6 M 1.0 M 3.0 M 6.0 M 10.0                   __________________________________________________________________________                                                             M                      0.25M ADOGEN 383 IN > 2 × 10.sup.3                                                                 > 2 × 10.sup.3                                                                 > 2 × 10.sup.3                                                                 > 2 × 10.sup.3                                                                 1 × 10.sup.3                                                                   4.8 × 10.sup.2                                                                 9.8 ×                                                                    10.sup.0               SOLVESSO 150                                                                   0.25M ADOGEN 383 + 50% 2-ETHYL                                                 HEXANOIC ACID IN SOLVESSO 150                                                                      8.8 × 10.sup.0                                                                 1.5 × 10.sup.1                                                                 8.1 × 10.sup.0                                                                 3.8 × 10.sup.0                                                                 7.3 × 10.sup.-1                                                                2.5 × 10.sup.-1                                                                2.5 ×                                                                    10.sup.-1              0.25M ADOGEN 383 IN                                                            2-ETHYLHEXANOIC ACID      3.9 × 10.sup.0                                                                 2.9 × 10.sup.0                                                                 1.4 × 10.sup.0                                                                             1.05 ×                                                                   10.sup.-1              0.25M ADOGEN 383 + 50%                                                         OCTANOIC ACID IN SOLVESSO 150                                                                      9.0 × 10.sup.0                                                                 1.2 × 10.sup.1                                                                 6.9 × 10.sup.0                                                                 2.9 × 10.sup.0                                                                 6.2 × 10.sup.-1                                                                2.2 × 10.sup.-1                                                                2.3 ×                                                                    10.sup.-1              0.25M ADOGEN 383 + 50%                                                         VERSATIC                                                                       911 ACID IN SOLVESSO 150                                                                           5.5 × 10.sup.1                                                                 5.8 × 10.sup.1                                                                 1.9 × 10.sup.1                                                                 9.9 × 10.sup.0                                                                 2.7 × 10.sup.0                                                                 1.1 × 10.sup.0                                                                 5.2 ×                                                                    10.sup.-1              0.25M ADOGEN 383 + 50% 2-ETHYL-                                                HEXANOL IN SOLVESSO 150                                                                            1.6 × 10.sup.2                                                                 1.3 × 10.sup.2                                                                 2.1 × 10.sup.1                                                                 8.4 × 10.sup.0                                                                 1.6 × 10.sup.0                                                                 2.0 × 10.sup.0                                                                 2.1 ×                                                                    10.sup.0               0.25M ADOGEN 383 + 10%                                                         NONYLPHENOL IN SOLVESSO 150                                                                        4.4 × 10.sup.1                                                                 4.3 × 10.sup.1                                                                 1.6 × 10.sup.1                                                                 7.9 × 10.sup.0                                                                 1.7 × 10.sup.0                                                                 5.4 × 10.sup.0                                                                 5.5 ×                                                                    10.sup.0               0.25M ADOGEN 383 + 15%                                                         NONYLPHENOL IN SOLVESSO 150                                                                        1.9 × 10.sup.1                                                                 2.1 × 10.sup.1                                                                 5.3 × 10.sup.0                                                                 2.0 × 10.sup.0                                                                 3.2 × 10.sup.-1                                                                1.4 × 10.sup.-1                                                                1.15 ×                                                                   10.sup.-1              0.25M ADOGEN 383 + 25%                                                         NONYLPHENOL IN SOLVESSO 150                                                                        6.1 × 10.sup.0                                                                 6.3 × 10.sup.0                                                                 1.2 × 10.sup.0                                                                 3.1 × 10.sup.-1                                                                4.6 × 10.sup.-2                                                                1.6 × 10.sup.-2                                                                1.3 ×                                                                    10.sup.-2              __________________________________________________________________________      ALL % ARE w/v %                                                          

Example 2-EFFECT OF MODIFIERS ON ALAMINE 336

The hydrogen bonding modifiers investigated in this example are selected from those listed in Table 1, viz, alcohols, carboxylic acids and phenols with a wide range of carbon-chain structures and molecular weights. In order to determine the maximum possible effect of each modifier the first experiments were carried out on solutions where the modifier was used as the only diluent present. The mole ratio of amine to modifier was calculated from the weight of each used. In cases where the modifier was a solid at room temperature a saturated solution in Solvesso 150 was used as diluent.

Experimental

Distribution data was obtained for platinum (IV) as described in Example 1 above, using 0.25 M solutions (9.8% w/v) of Alamine 336 in the appropriate modifier or modifier/Solvesso combination. The results are recorded in Table 3.

                                      TABLE 3                                      __________________________________________________________________________     DISTRIBUTION COEFFICIENTS FOR Pt (IV) USING ALAMINE 336 IN THE PRESENCE        OF MODIFIERS                                                                            AMINE:                                                                         MODIFIER                                                                              Diluent if                                                                            MOLARITY OF HCl SOLUTION                                MODIFIER Molar Ratio                                                                           Required                                                                              0.1 M                                                                               0.3 M                                                                               0.6 M                                                                               1 M  3 M  6 M  8 M  10                   __________________________________________________________________________                                                               M                    None       --   Solvesso 150                                                                          >2×10.sup.3                                                                   >2×10.sup.3                                                                   >2×10.sup.3                                                                   >2×10.sup.3                                                                   >2×10.sup.3                                                                   6.9×10.sup.2                                                                  9.9×10.sup.1                                                                  1.3×10.sup                                                               .1                   Hexan-1-ol                                                                              1:27.4 --     4.8×10.sup.0                                                                  1.6×10.sup.2                                                                  2.9×10.sup.1                                                                  1× 10.sup.1                                                                   4.7×10.sup.1                                                                  5.3×10.sup.0                                                                  4.5×10.sup.0                                                                  3.5×10.sup                                                               .0                   Octan-1-ol                                                                              1:22   --     4.9×10.sup.0                                                                  7.5×10.sup.1                                                                  2.6×10.sup.1                                                                  5.8×10.sup.0                                                                  3.2×10.sup.0                                                                  3.1×10.sup.0                                                                  2.8×10.sup.0                                                                  3.5×10.sup                                                               .0                   Dodecanol                                                                               1:10   Solvesso 150                                                                          1.1×10.sup.1                                                                  4.7×10.sup.2                                                                  7.7×10.sup.1                                                                  1.9×10.sup.1                                                                  2.8×10.sup.0                                                                    *    *  2.6×10.sup                                                               .0                   2-Ethylbutanol                                                                          1:22   --     5.4×10.sup.0                                                                  2.4×10.sup.0                                                                  1.6×10.sup.1                                                                  5.4×10.sup.0                                                                  2.1×10.sup.0                                                                  3×10.sup.0                                                                    2.4×10.sup.0                                                                  2×10.sup.0     2-Ethylhexanol                                                                          1:22   --     1.9×10.sup.2                                                                  1.4×10.sup.2                                                                  1.8×10.sup.1                                                                  4.8×10.sup.0                                                                  1.9×10.sup.0                                                                  2.5×10.sup.0                                                                  3×10.sup.0                                                                    2.6×10.sup                                                               .0                   3,5,5-Trimethyl-                                                               hexanol  1:20   --     >2×10.sup.3                                                                   >2×10.sup.3                                                                   2.4×10.sup.1                                                                  1.8×10.sup.1                                                                  1.6×10.sup.0                                                                  2.8×10.sup.0                                                                  3.2×10.sup.0                                                                  2.8×10.sup                                                               .0                   Tridecanol                                                                              1:14.9 --     8.8×10.sup.0                                                                  9.8×10.sup.1                                                                  2.6×10.sup.1                                                                  7.5×10.sup.0                                                                  2.5×10.sup.0                                                                  3.2×10.sup.0                                                                  3.2×10.sup.0                                                                  6.7×10.sup                                                               .0                   Octan-2-ol                                                                              1:22   --     6.7×10.sup.0                                                                  1.3×10.sup.2                                                                  1.1×10.sup.1                                                                  1.1×10.sup.1                                                                  2.6×10.sup.0                                                                  2.5×10.sup.0                                                                  2.1×10.sup.0                                                                  1.4×10.sup                                                               .0                   4-Methylpentan-                                                                2-ol     1:25   --     6.3×10.sup.0                                                                  5.0×10.sup.2                                                                  2.9×10.sup.1                                                                  8.1×10.sup.0                                                                  2.9×10.sup.0                                                                  2.5×10.sup.0                                                                  1.9×10.sup.0                                                                  1.2×10.sup                                                               .0                   t-Pentanol                                                                              1:32   --     5.3×10.sup.0                                                                  1.7×10.sup.2                                                                  5.5×10.sup.1                                                                  1.5×10.sup.0                                                                  7.1×10.sup.0                                                                  5.3×10.sup.0                                                                  2.8×10.sup.0                                                                  2.9×10.sup                                                               .0                   Cyclohexanol                                                                            1:33   --     5.5×10.sup.0                                                                  7.3×10.sup.1                                                                  1.9×10.sup.1                                                                  7.8×10.sup.0                                                                  6.2×10.sup.0                                                                  4.1×10.sup.2                                                                    +    +                  3,3,5-Trimethyl-                                                               cyclohexanol                                                                            1:21   --     >2×10.sup.3                                                                   >2×10.sup.3                                                                   7.6×10.sup.1                                                                  2.8×10.sup.1                                                                  1.2×10.sup.1                                                                  6.9×10.sup.0                                                                  4.7×10.sup.0                                                                  2.5×10.sup                                                               .0                   Hexanoic acid                                                                           1:28   --     1.6×10.sup.0                                                                  2.7×10.sup.0                                                                  1.4×10.sup.0                                                                  4.7×10.sup.-1                                                                 6×10.sup.-2                                                                   1.5×10.sup.-1                                                                 2.5×10.sup.-1                                                                 4.5×10.sup                                                               .-1                  Hexanoic acid                                                                           1:20   Solvesso 150                                                                          2.5×10.sup.0                                                                  6.6×10.sup.0                                                                  3.7×10.sup.0                                                                  1.5×10.sup.0                                                                  2.6×10.sup.-1                                                                 1.5×10.sup.-1                                                                 1.6×10.sup.-1                                                                 2.6×10.sup                                                               .-1                  Octanoic acid                                                                           1:22   --     1.5×10.sup.0                                                                  4.6×10.sup.0                                                                  2.7×10.sup.0                                                                  8.9×10.sup.-1                                                                 1.9×10.sup.-1                                                                 1.2×10.sup.-1                                                                 1×10.sup.-1                                                                   2.5×10.sup                                                               .-1                  Octanoic acid                                                                           1:15   Solvesso 150                                                                          5.1×10.sup.0                                                                  2.6×10.sup.0                                                                  4.2×10.sup.0                                                                  3.3×10.sup.0                                                                  1.2×10.sup.0                                                                  8.2×10.sup.-1                                                                 1×10.sup.0                                                                    1.1×10.sup                                                               .0                   Dodecanoic acid                                                                         1:8.5  Solvesso 150                                                                          >2×10.sup.3                                                                   >2×10.sup. 3                                                                  1.8×10.sup.1                                                                  1.3×10.sup.1                                                                  2.6×10.sup.0                                                                  1.5×10.sup.0                                                                  1.5×10.sup.0                                                                  1.4×10.sup                                                               .0                   2-Ethylhexanoic                                                                acid     1:22   --     1.1×10.sup.1                                                                  7.2×10.sup.0                                                                  4.7×10.sup.0                                                                  2×10.sup.0                                                                    6.1×10.sup.-1                                                                 3.1×10.sup.-1                                                                 5×10.sup.-1                                                                   7×10.sup.-                                                               1                    2-Ethylhexanoic                                                                acid     1:15   Solvesso 150                                                                          >2×10.sup.3                                                                   >2×10.sup.3                                                                   >2×10.sup.3                                                                   7.9×10.sup.1                                                                  1.8×10.sup.0                                                                  9.8×10.sup.1                                                                  1.8×10.sup.1                                                                  7.9×10.sup                                                               .1                   3,3,5 Trimethyl-                                                               hexanoic acid                                                                           1:20   --     1.7×10.sup.0                                                                  7.5×10.sup.0                                                                  5.2×10.sup.0                                                                  1.7×10.sup.0                                                                  3.5×10.sup.-1                                                                 2.2×10.sup.-1                                                                 2.7×10.sup.-1                                                                 8.9×10.sup                                                               .-1                  3,3,5 Trimethyl-                                                               hexanoic acid                                                                           1:15   Solvesso 150                                                                          2.9×10.sup.0                                                                  1.5×10.sup.1                                                                  9.3×10.sup.0                                                                  3.2×10.sup.0                                                                  9.8×10.sup.-1                                                                 7.0×10.sup.-1                                                                 8.9×10.sup.-1                                                                 5.6×10.sup                                                               .-1                  Versatic acid                                                                           1:19   --     >2×10.sup.3                                                                   >2×10.sup.3                                                                   1.3×10.sup.0                                                                  7×10.sup.0                                                                    1.3×10.sup.0                                                                  1×10.sup.0                                                                    1.6×10.sup.0                                                                  8.9×10.sup                                                               .-1                  Napthenic acid                                                                          1:18   --     6.3×10.sup.0                                                                  1.6×10.sup.1                                                                  8.8×10.sup.0                                                                  5×10.sup.0                                                                    9.6×10.sup.-1                                                                 5.2×10.sup.-1                                                                 6.6×10.sup.-1                                                                 1.3×10.sup                                                               .0                   NonylPhenol                                                                             1:14.8 --     4.9×10.sup.-1                                                                 1.0×10.sup.0                                                                  4.1×10.sup.-2                                                                 2×10.sup.-2                                                                   1.5×10.sup.-1                                                                 1.2×10.sup.-1                                                                 1.0×10.sup.-1       NonylPhenol                                                                             1:10   Solvesso 150                                                                          1.3×10.sup.0                                                                  3.0×10.sup.0                                                                  4.9×10.sup.-1                                                                 1.9×10.sup.-1                                                                 1.9×10.sup.-1                                                                 5.2×10.sup.-2                                                                 1.9×10.sup.-1                                                                 3.6×10.sup                                                               .-1                  NonylPhenol                                                                             1:5    Solvesso 150                                                                          2.3×10.sup.0                                                                  1.9×10.sup.0                                                                  1.9×10.sup.0                                                                  1.5×10.sup.0                                                                  3.3×10.sup.-1                                                                 1.2×10.sup.-1                                                                 5.8×10.sup.-2                                                                 1.0×10.sup                                                               .-1                  NonylPhenol                                                                             2:5    Solvesso 150                                                                          3.5×10.sup.0                                                                  2.5×10.sup.1                                                                  9×10.sup.0                                                                    8.1×10.sup.0                                                                  7.4×10.sup.0                                                                  5.4×10.sup.-1                                                                 7.8×10.sup.-1                                                                 7.3×10.sup                                                               .-1                  2,4 Di-t-butyl-                                                                Phenol   1:10   Solvesso 150                                                                          5.2×10.sup.-1                                                                 3.2×10.sup.-1                                                                 1.1×10.sup.-1                                                                 4.3×10.sup.-2                                                                 1.1×10.sup.-2                                                                 4.5×10.sup.-2                                                                 5.0×10.sup.-2                                                                 3.7×10.sup                                                               .-2                  2,4 Di-t-butyl-                                                                Phenol   1:5    Solvesso 150                                                                          1.1×10.sup.0                                                                  2.4×10.sup.0                                                                  8.9×10.sup.-1                                                                 2.0×10.sup.-1                                                                 2.2×10.sup.-2                                                                 4.5×10.sup.-2                                                                 5.0×10.sup.-2                                                                 1.4×10.sup                                                               .-3                  2,4 Di-t-butyl-                                                                Phenol   1:2    Solvesso 150                                                                          3.5×10.sup.0                                                                  2.3×10.sup.1                                                                  1.1×10.sup.1                                                                  3.6×10.sup.0                                                                  1.2×10.sup.0                                                                  6.4×10.sup.-1                                                                 5.1×10.sup.-1                                                                 4.3×10.sup                                                               .-1                  __________________________________________________________________________      Key                                                                            *Emulsion formed                                                               + Phases did not separate i.e. no aqueous sample recovered               

The results indicate that all the acids investigated act as effective modifiers in the Alamine 336 system. Those exhibiting the most pronounced effect were:

    ______________________________________                                         Ratio           D.sub.A.sup.o (0.3M HCl)                                                                    D.sub.A.sup.o (6M HCl)                            ______________________________________                                         1:22 Octanoic acid  4.6 × 10.sup.0                                                                        1.2 × 10.sup.-1                         1:20 Hexanoic acid  6.6 × 10.sup.0                                                                        1.5 × 10.sup.-1                         1:22 2-Ethylhexanoic acid                                                                          7.2 × 10.sup.0                                                                        3.1 × 10.sup.-1                         1:20 3,5,5 Trimethyl                                                                hexanoic acid  7.5 × 10.sup.0                                                                        2.2 × 10.sup.-1                         ______________________________________                                    

The changes in distribution coefficient in the case of these four modifiers quoted above enable acid stripping to be carried out when Alamine 336 is used as the extractant. The alcohols tested have a similar effect on the system but to a much lesser degree. The two phenols included in the investigation showed promise in that they depress the distribution coefficient at a much lower extractant/modifier ratio, i.e., 1:2, than is required for acids (1:20). See table 4 below.

                  TABLE 4                                                          ______________________________________                                         Ratio          D.sub.A.sup.o (0.3M HCl)                                                                    D.sub.A.sup.o (6M HCl)                             ______________________________________                                         2:5Nonylphenol 2.5 × 10.sup.1                                                                        5.4 × 10.sup.-1                              1:2 2,4-Di-t-butylphenol                                                                      2.3 × 10.sup.1                                                                        6.4 × 10.sup.-1                              1:5 Nonyl Phenol                                                                              1.9 × 10.sup.0                                                                        1.26 × 10.sup.-1                             1:5 2,4-Di-t-butylphenol                                                                      2.4 × 10.sup.0                                                                        4.5 × 10.sup.-2                              ______________________________________                                    

At a 1:2 ratio for either phenol, extraction was good but acid stripping less satisfactory. However, when the phenol ratio was increased to 1:5, a more effective acid strip was achieved but extraction was impaired. The optimum ratio lies within these limits, for example 1:3 to 1:4.

The diluent used was Solvesso 150 with a composition of 99.7% aromatic and 0.3% paraffinic. Alternative diluents are Escaid 100 (20% Aromatic, 56.6. paraffinic and 23.6% Naphthenic), MSB 210 (2.5% Aromatic 97.5% paraffinic) and Isopar L(100% paraffinic).

Example 3 EFFECT OF DILUENT ON THE MODIFIED ALAMINE 336 SYSTEM

The work on the Alamine 336 was extended to investigate the effect of different diluents on the distribution co-efficient of the amine: modifier system. The systems which showed most promise when Solvesso 150 was used as diluent, were repeated using Isopar L, Escaid and MSB 210 as diluents.

The modifiers selected were

    ______________________________________                                         1. Hexanoic acid     Mole Ratio 1:20                                           2. 2 Ethyl hexanoic acid                                                                            Mole Ratio 1:20                                           3. Octanoic acid     Mole Ratio 1:20                                           4. 2,4 Di-t-Butylphenol                                                                             Mole Ratio 1:2                                            5. Nonylphenol       Mole Ratio 2:5                                            ______________________________________                                    

In the case of the acids, the amount of diluent added was relatively small (10-15%) and only a small effect was found.

However, in the case of the phenols, (where the diluent constitutes more than 50% of extradent) the change did have a more marked effect, especially for Nonylphenol. The results are illustrated graphically in FIGS. 1-5 of the accompanying drawings.

Example 4-FURTHER INVESTIGATION OF MODIFIERS ON THE ADOGEN 383 SYSTEM

A similar investigation to that carried out using Alamine 336 was also carried out using Adogen 383. The conditions in each case were identical to those of Example 1, but only a cross-section of the alcohols was investigated.

The results are given in Table 5.

                                      TABLE 5                                      __________________________________________________________________________     Distribution Coefficients of Pt (IV) Using Adogen 383 in the                   Presence of Modifiers                                                                    AMINE:                                                                         MODI-                                                                          FIER DILUENT                                                                   MOLAR                                                                               IF     ACID MOLARITY OF SOLUTION                                MODIFIER  RATIO                                                                                REQUIRED                                                                             0.1M 0.3M 0.6M 1M    3M   6M   8M   10M                  __________________________________________________________________________     None           Solvesso 150                                                                          >2×10.sup.3                                                                   >2×10.sup.3                                                                   >2×10.sup.3                                                                   >2×10.sup.3                                                                    1×10.sup.3                                                                    4.8×10.sup.2                                                                  9.9×10.sup.1                                                                  9.8×10.sup                                                               .0                   Hexan-1-ol                                                                               1:21 --     3.2×10.sup.0                                                                  4.4×10                                                                        1.2×10.sup.1                                                                  5×10.sup.0                                                                     3×10.sup.0                                                                    4.7×10.sup.0                                                                  3.6×10.sup.0                                                                  3×10.sup.0     2-Ethylhexanol                                                                           1:21 --     8.2×10.sup.1                                                                  7×10.sup.1                                                                    1.2×10.sup.1                                                                  4.6×10.sup.0                                                                   1.5×10.sup.0                                                                  2×10.sup.0                                                                    2.3×10.sup.0                                                                  2.3×10.sup                                                               .0                   3,5,5-Trimethyl-                                                               hexanol   1:14 --     4.1×10.sup.0                                                                  1×10.sup.2                                                                    1.9×10.sup.1                                                                  7.8×10.sup.0                                                                   2×10.sup.0                                                                    4.1×10.sup.0                                                                  3.6×10.sup.0                                                                  2.8×10.sup                                                               .0                   Cyclohexanol                                                                             1:31 --     3.8×10.sup.0                                                                  6.3×10.sup.1                                                                  2×10.sup.1                                                                    9×10.sup.0                                                                     5.2× 10.sup.0                                                                 4.9×10.sup.0                                                                  2.6×10.sup.0                                                                    --                 2-Ethylhexan-                                                                  1,3 diol  1:21 --     2.9×10.sup.0                                                                  1.8×10.sup.1                                                                  6.8×10.sup.0                                                                  2.8×10.sup.0                                                                   2.2×10.sup.0                                                                  5.8×10.sup.0                                                                    --   --                 3,5,5-trimethyl-                                                               cyclohexanol                                                                             1:20 --     3.9×10.sup.0                                                                  1.3×10.sup.2                                                                  2.1×10.sup.1                                                                  1.6×10.sup.1                                                                   3.2×10.sup.0                                                                  3.8×10.sup.0                                                                  3.4×10.sup.0                                                                  2.1×10.sup                                                               .0                   Octanoic acid                                                                            1:20 --     1×10.sup.0                                                                    3.4×10.sup.0                                                                  1.9×10.sup.0                                                                  6.6×10.sup.-1                                                                  9.8×10.sup.-2                                                                 3.0×10.sup.-2                                                                 7.5×10.sup.-2                                                                 7.5×10.sup                                                               .-2                  Octanoic acid                                                                            1:15 Solvesso 150                                                                          1.6×10.sup.0                                                                  9.0×10.sup.0                                                                  4.3×10.sup.0                                                                  1.5×10.sup.0                                                                   3.1×10.sup.-1                                                                 2.9×10.sup.-1                                                                 2×10.sup.-1                                                                   1.6×10.sup                                                               .-1                  2-Ethylhexanoic                                                                acid      1:20 --     1×10.sup.0                                                                    9.3×10.sup.0                                                                  2.2×10.sup.0                                                                  1.2×10.sup.0                                                                   4×10.sup.-1                                                                   1.9×10.sup.-1                                                                 3.1×10.sup.-1                                                                 1.2×10.sup                                                               .-1                  2-Ethylhexanoic                                                                acid      1:15 Solvesso 150                                                                          1.4×10.sup.0                                                                  9.5×10.sup.0                                                                  5.7×10.sup.0                                                                  2.4×10.sup.0                                                                   6.6×10.sup.-1                                                                 3.3×10.sup.-1                                                                 3.3×10.sup.-                                                                  2.9×10.sup                                                               .-1                  Hexanoic acid                                                                            1:26 --     1×10.sup.0                                                                    3×10.sup.0                                                                    1.3×10.sup.0                                                                  6×10.sup.-1                                                                    1.1×10.sup.-1                                                                 2.5×10.sup.-1                                                                 2.5×10.sup.-1                                                                 1.4×10.sup                                                               .0                   Hexanoic acid                                                                            1:20 Solvesso 150                                                                          1×10.sup.0                                                                    4.4×10.sup.0                                                                  2.2×10.sup.0                                                                  9.2×10.sup.-1                                                                  2.0×10.sup.-1                                                                 1.2×10.sup.-1                                                                 2.1×10.sup.-1                                                                 1.5×10.sup                                                               .-1                  Naphthenic acid                                                                          1:17 --     1.3×10.sup.0                                                                  2.3×10.sup.0                                                                  3×10.sup.0                                                                    1.6×10.sup.0                                                                   5.7×10.sup.-1                                                                 3.7×10.sup.-1                                                                 3.9×10.sup.-1                                                                 4.1×10.sup                                                               .-1                  3,5,5-Trimethyl-                                                               hexanoic acid                                                                            1:18 --     1.1×10.sup.0                                                                  3.2×10.sup.0                                                                  1.3×10.sup.0                                                                  8.2×10.sup.-1                                                                  2.8×10.sup.-1                                                                 1.2×10.sup.-1                                                                 1.2×10.sup.0                                                                  1.4×10.sup                                                               .-1                  Dodecanoic acid                                                                          1:5  Solvesso 150                                                                          4×10.sup.0                                                                    7.4×10.sup.1                                                                  3.5×10.sup.1                                                                  1.5×10.sup.1                                                                   2.6×10.sup.0                                                                  1.2×10.sup.0                                                                  1.2×10.sup.0                                                                  7.7×10.sup                                                               .-1                  Versatic acid                                                                            1:17 --     2.5×10.sup.0                                                                  2.2×10.sup.1                                                                  1.0×10.sup.1                                                                  2.3×10.sup.0                                                                   6.1×10.sup.-1                                                                 4.3×10.sup.-1                                                                 3.9×10.sup.-1                                                                 5.4×                                                                     10.sup.-1            2-Ethylbutyric                                                                 acid      1:26 --     7.3×10.sup.-1                                                                 2.4×10.sup.0                                                                  1.4×10.sup.0                                                                  5.26×10.sup.-1                                                                 5.2×10.sup.-2                                                                 3×10.sup.-2                                                                   8.6×10.sup.-2                                                                 1.6×10.sup                                                               .-1                  2,4-di-t-butyl-                                                                phenol    1:5  Solvesso 150                                                                          9.2×10.sup.-1                                                                 1.8×10.sup.0                                                                  3.3×10.sup.-1                                                                 2.2×10.sup.-1                                                                  7.5×10.sup.-2                                                                 2×10.sup.-2                                                                   3.1×10.sup.-2                                                                 5.2×10.sup                                                               .-1                  Nonylphenol                                                                              1:5  Solvesso 150                                                                          6.1×10.sup.0                                                                  6.3×10.sup.0                                                                  1.2×10.sup.0                                                                  3.1×10.sup.-1                                                                  4.6×10.sup.-2                                                                 1.6×10.sup.-2                                                                   -- 1.3×10.sup                                                               .-2                  Nonylphenol                                                                              1:3  Solvesso 150                                                                          1.9×10.sup.1                                                                  2.1×10.sup.1                                                                  5.3×10.sup.0                                                                  2.0×10.sup.0                                                                   3.2×10.sup.-1                                                                 1.4×10.sup.-1                                                                   -- 1.3×10.sup                                                               .-1                  Nonylphenol                                                                              1:2  Solvesso 150                                                                          3×10.sup.0                                                                    4.8×10.sup.1                                                                  1.6×10.sup.1                                                                  4.9×10.sup.0                                                                   1.4×10.sup.0                                                                  8.2×10.sup.-1                                                                 7.4×10.sup.-1                                                                 4.3×10.sup                                                               .-1                  __________________________________________________________________________

Example 5--EFFECT OF MODIFIERS ON THE AMBERLITE LA2 SYSTEM

A similar investigation to that of Example 4 was carried out using Amberlite LA2, a secondary amine. The conditions in each case were identical with those of Example 1, representative modifiers only being evaluated.

The results are given in Table 6.

                                      TABLE 6                                      __________________________________________________________________________     DISTRIBUTION COEFFICIENTS FOR THE EXTRACTION OF Pt (IV) USING 0.25M            AMBERLITE                                                                      LA2 IN SOLVESSO 150 IN THE PRESENCE OF MODIFIERS                                       AMINE                                                                          MODI-                                                                          FIER                                                                           MOLAR                                                                               ACID MOLARITY OF SOLUTION                                         MODIFIER                                                                               RATIO                                                                               0.1   0.3   0.6   1     3     6      8      10                    __________________________________________________________________________     None    --   5.2 × 10.sup.1                                                                 9.9 × 10.sup.1                                                                 3.6 × 10.sup.1                                                                 1.6 × 10.sup.1                                                                 3.9 × 10.sup.0                                                                 1.7 × 10.sup.0                                                                  1.0 × 10.sup.0                                                                  4.2 ×                                                                    10.sup.-1             Octanoic Acid                                                                          1:1  1.3 × 10.sup.1                                                                 4.6 × 10.sup.1                                                                 6.7 × 10.sup.0                                                                 4.9 × 10.sup.0                                                                 1.1 × 10.sup.0                                                                 6 × 10.sup.-1                                                                   4.5 × 10.sup.-1                                                                 2.5 ×                                                                    10.sup.-1             Octanoic Acid                                                                          1:2  4.7 × 10.sup.0                                                                 4 × 10.sup.1                                                                   1 × 10.sup.1                                                                   4.5 × 10.sup.0                                                                 8 × 10.sup.-1                                                                  3.8 × 10.sup.-1                                                                 3.3 × 10.sup.-1                                                                 1.9 ×                                                                    10.sup.-1             Octanoic Acid                                                                          1:3  3.5 × 10.sup.0                                                                 2.6 × 10.sup.1                                                                 7.8 × 10.sup.0                                                                 2.8 × 10.sup.0                                                                 6 × 10.sup.-1                                                                  3.1 × 10.sup.-1                                                                 2.5 × 10.sup.-1                                                                 2.3 ×                                                                    10.sup.-1             Octanoic Acid                                                                          1:4  2 8 × 10.sup.0                                                                 2.2 × 10.sup.1                                                                 7.0 × 10.sup.0                                                                 4 × 10.sup.0                                                                   3 × 10.sup.0                                                                   2 × 10.sup.-1                                                                   1.7 × 10.sup.-1                                                                 8.1 ×                                                                    10.sup.-1             Dodecyl Phenol                                                                         2:1  5.3 × 10.sup.0                                                                 3.7 × 10.sup.1                                                                 1.2 × 10.sup.1                                                                 4 × 10.sup.0                                                                   1 × 10.sup.0                                                                   5.5 × 10.sup.-1                                                                 3.8 × 10.sup.-1                                                                 2.3 ×                                                                    10.sup.-1             Nonyl Phenol                                                                           2:1  2.9 × 10.sup.0                                                                 4.4 × 10.sup.1                                                                 1.3 × 10.sup.1                                                                 5.5 × 10.sup.0                                                                 1 × 10.sup.0                                                                   6.2 × 10.sup.-1                                                                 4.4 × 10.sup.-1                                                                 2 ×                                                                      10.sup.-1             2,4Di-t-Butyl-                                                                 phenol  2:1  2.9 × 10.sup.0                                                                 4.6 ×  10.sup.1                                                                1.4 × 10.sup.1                                                                 4.9 × 10.sup.0                                                                 1 × 10.sup.0                                                                   6.7 × 10.sup.-1                                                                 5.6 × 10.sup.-1                                                                 3.1 ×                                                                    10.sup.-1             Nonylphenol                                                                            4:3  2.3 × 10.sup.0                                                                 3.1 × 10.sup.1                                                                 7.5 × 10.sup.0                                                                 2.7 × 10.sup.0                                                                 6.5 × 10.sup.-1                                                                6.5 × 10.sup.-1                                                                 3.1 × 10.sup.-1                                                                 2.1 ×                                                                    10.sup.-1             Nonylphenol                                                                            1:1  1.8 × 10.sup.0                                                                 1.56 × 10.sup.0                                                                4.7 × 10.sup.0                                                                 1.4 × 10.sup.0                                                                 3.8 × 10.sup.-1                                                                2.5 × 10.sup.-1                                                                 2.5 × 10.sup.-1                                                                 3 ×                                                                      10.sup.-1             2,4Di-t-Butyl-                                                                 phenol  1:1  1.56 × 10.sup.1                                                                4.5 × 10.sup.0                                                                 3.5 × 10.sup.0                                                                 1.4 × 10.sup.0                                                                 3.6 × 10.sup.-1                                                                1.6 × 10.sup.-1                                                                 1.36 × 10.sup.-1                                                                1.4 ×                                                                    10.sup.-1             Hexanoic Acid                                                                          1:4  2.8 × 10.sup.0                                                                 1.95 × 10.sup.1                                                                4.7 × 10.sup.0                                                                 1.8 × 10.sup.0                                                                 3.6 × 10.sup.                                                                  2.2 × 10.sup.-1                                                                 2.2 × 10.sup.-1                                                                 2.1 ×                                                                    10.sup.-1             3,5,5, Trimethyl                                                               Hexanoic Acid                                                                          1:4  3.4 × 10.sup.0                                                                 1.8 × 10.sup.1                                                                 5.2 × 10.sup.0                                                                 2 × 10.sup.0                                                                   3.5 × 10.sup.-1                                                                1.8 × 10.sup.-1                                                                 1.6 × 10.sup.-1                                                                 1.5 ×                                                                    10.sup.-1             2 Ethylhexanoic                                                                Acid    1:4  2.6 × 10.sup.0                                                                 1.9 × 10.sup.1                                                                 5.9 × 10.sup.0                                                                 2.2 × 10.sup.0                                                                 3.9 × 10.sup.-1                                                                2.4 × 10.sup.-1                                                                 2.1 × 10.sup.-1                                                                 1.8 ×                                                                    10.sup.-1             2 Ethyl hexanol                                                                         1:10                                                                               1.3 × 10.sup.1                                                                 6.7 × 10.sup.0                                                                 3.6 × 10.sup.0                                                                 1.2 × 10.sup.0                                                                 4.8 × 10.sup.-1                                                                6.3 × 10.sup.-1                                                                   --   7.1 ×                                                                    10.sup.-1             __________________________________________________________________________

Example 6--EFFECT OF MODIFIERS ON THE EXTRACTION OF IRIDIUM (IV)

Stock solutions containing 10 gl⁻¹ Ir (IV) in 0.1, 0.5, 1, 5 and 10 M hydrochloric acid were prepared from sodium hexachloroiridate (IV) and standardised acid. Aliquots of these solutions were contacted with equal volumes of the organic phases listed in Table 7 for two minutes. The aqueous phases were separated and analysed for iridium by atomic absorption spectrophotometry. From the analyses, the concentrations in the organic phase were determined by difference and the distribution coefficients then calculated.

                                      TABLE 7                                      __________________________________________________________________________     DISTRIBUTION COEFFICIENTS FOR THE EXTRACTION OF Ir (IV) USING                  0.25M ALAMINE 336 IN SOLVESSO 150 IN THE PRESENCE OF MODIFIERS                         AMINE:                                                                         MODIFIER                                                                       MOLAR  HCl MOLARITY OF SOLUTION                                        MODIFIER                                                                               RATIO  0.1M  0.5M 1.0M  5.0M  10.0M                                    __________________________________________________________________________     None      --   3.6 × 10.sup.3                                                                 2.4 × 10.sup.2                                                                1.5 × 10.sup.2                                                                 1.2 × 10.sup.2                                                                 2.4 × 10.sup.1                     Octan-1-ol                                                                             1:22.3 1.1 × 10.sup.2                                                                 2.1 × 10.sup.1                                                                1.1 × 10.sup.1                                                                 6.8 × 10.sup.0                                                                 6.2 × 10.sup.0                     Octanoic Acid                                                                          1:20   3.3. × 10.sup.1                                                                6.5 × 10.sup.0                                                                2.6 × 10.sup.0                                                                 6.4 × 10.sup.-1                                                                9.8 × 10.sup.-1                    4-nonylphenol                                                                          1:5    5.5 × 10.sup.0                                                                 1.3 × 10.sup.0                                                                5.3 × 10.sup.-1                                                                2.0 × 10.sup.-1                                                                1.3 × 10.sup.-1                    __________________________________________________________________________

Example 7--EFFECT OF MODIFIERS ON THE EXTRACTION OF PALLADIUM (II)

Stock solutions containing 10 gl⁻¹ Pd (II) in 0.1, 0.5, 1, 5 and 10 M hydrochloric acid were prepared from sodium tetrachloropalladate (II) and standardised acid. Aliquots of these solutions were contacted with equal volumes of the organic phases listed in Table 8 for two minutes. The aqueous phases were separated and analysed for palladium by atomic absorption spectrophotometry. From the analyses, the concentrations in the organic phase were determined by difference and the distribution coefficients then calculated.

                                      TABLE 8                                      __________________________________________________________________________     DISTRIBUTION COEFFICIENTS FOR THE EXTRACTION OF Pd (II) USING                  0.3M AMBERLITE LA2 IN SOLVESSO 150 IN THE PRESENCE OF MODIFIERS                        AMINE                                                                          MODIFIER                                                                       MOLAR  HCl MOLARITY OF SOLUTION                                        MODIFIER                                                                               RATE   0.1M 0.5M 1.0M  5.0M  10.0M                                     __________________________________________________________________________     None    --     1.9 × 10.sup.3                                                                1.5 × 10.sup.2                                                                4.7 × 10.sup.1                                                                 3.8 × 10.sup.0                                                                 7.1 × 10.sup.-1                     Octan-1-ol                                                                             1:6    1.2 × 10.sup.2                                                                7.4 × 10.sup.0                                                                8.9 × 10.sup.-1                                                                2.8 × 10.sup.-1                                                                1.6 × 10.sup.-1                     Octanoic Acid                                                                          1:4    5.9 × 10.sup.1                                                                1.1 × 10.sup.1                                                                4.5 × 10.sup.0                                                                 5.4 × 10.sup.-1                                                                3.2 × 10.sup.-1                     4-nonylphenol                                                                          1:1    6.7 × 10.sup.1                                                                7.3 × 10.sup.0                                                                2.8 × 10.sup.0                                                                 3.2 × 10.sup.-1                                                                1.9 × 10.sup.-1                     __________________________________________________________________________ 

I claim:
 1. A process for the separation or purification of platinum group metals in which either platinum, iridium (IV) and/or palladium (II) are present in aqueous solution together with at least one of rhodium and ruthenium and one or more base metals comprising the steps of:(a) contacting the said aqueous solution of a pH of less than 1 with an organic hydrocarbon extraction solvent containing at least one nitrogen containing organic compound selected from the group consisting of primary, secondary and tertiary amines and quarternary ammonium compounds and at least one oxygen containing organic compound selected from the group consisting of alcohols, phenols and carboxylic acids; (b) removing from contact with the said aqueous solution the said organic phase now containing the platinum, iridium (IV) and/or palladium (II) extracted from the aqueous solution together with the nitrogen- and oxygen-containing organic compounds while leaving other platinum group metals and base metals in the aqueous solution; and (c) contacting the organic phase obtained at stage (b) above with an aqueous solution of a strong acid and thus stripping the platinum, iridium and/or palladium from the said organic phase and obtaining an aqueous solution of the said metals.
 2. A process according to claim 1 wherein the nitrogen containing organic compound used in step (a) is a branched chain secondary amine of general formula R₂ NH in which R is aliphatic.
 3. A process according to claim 2 wherein R is C₁₂ -C₁₄ alkyl.
 4. A process according to claim 2 wherein the nitrogen containing organic compound in step (a) is equilibrated with an acid before contacting with the acidified solution.
 5. A process according to claim 2 wherein the R groups are the same or different and are selected from the group consisting of the normal and iso isomers of hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl alkyl groups.
 6. A process according to claim 2 wherein the secondary amines of step (a) are selected from the group consisting of N-dodecyl (trialkylmethyl) amine, N-lauryl (trialkylmethyl) amine, secondary amine mixtures and di-isotridecylamine.
 7. A process according to claim 1 wherein the solution of strong acid in step (c) is a strong HCl, HBr or HClO₄ solution.
 8. A process according to claim 1 wherein the tertiary amines in step (a) have a formula R₃ N where R is aliphatic.
 9. A process according to claim 8 wherein R is a normal alkyl group having a carbon range C₆ -C₁₄.
 10. A process according to claim 8 wherein the R groups are the same or different and are selected from normal and iso isomers of hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl alkyl groups.
 11. A process according to claim 8 wherein the R groups are selected from aromatic and mixed aliphatic aromatic groups. 